Method of purifying salt and recovering by-products



Jan. 1, I929.

v. YNGVE METHOD OF PURIFY IJNG .SALT AND RECOVERI'NG BY -PRODUICTS FiledApril 9 NSQ ants 553% gi v ESQ tutti INVENTOR A ATTORNEY Patented Jan.1, 1929.

PATENT OFFICE.

VICTOR YNGVE, OF SOUTH ORANGE, NEW JERSEY.

METHOD OF PUBIFYIN'G SALT AND RECOVERING BY-PRODUCTS.

Application filed April 9, 1925. Serial No. 21,844.

1,520,920 and is in part an extension of that invention.

.'The starting point of the process mvolved in the present invention isbrine, which may be of any suitable concentration but preferablycontains about 300 grams of sodium chloride per liter. --The' brinemaybe natural or artificial, made from any availablecommercial grade ofsalt and may be sub ected to pretreatment. A typical brine which may beused, though it is not to be considered in a limiting sense, is thefollowing:

Grams perliter. Sodium 114.0 Chlorine 174.2 Magnesium .8 Calcium p 1.4Sulphur trioxide 3.2

The process is best explained by means of the attached drawing, thoughit 15 understood that variations in the procedure will occur to thoseskilled in the art without departing from the-spirit of the invention.

The crude brine is treated in container I with sodium hydroxide. Thesodium hydroxide can be added in any suitable manner, but preferably themain portion of it is added just as it comes from XVI, causticchlorinecells, and salt is also present in the caustic solution. Sodiumhydroxide is also added from other parts of the process as will bedisclosed later. The sodium hydroxide is added in excess of the amountto precipitate the magnesium and calciumpresent in the brine. The amountmay vary from a fraction of one per cent to five per cent or more, butpreferably about 10 grams per liter is added. The mixture is preferablyheated to about 100 C.

or allowed to settle in II. The clear brine is stored in III from whichit goes to evaporators IV, V and VI.

In the evaporators the brine is concentrated and salt separates out.Sodium hydroxide and sodium sulphate become concentrated in the motherliquor. WVhen the sodium hydroxide concentration reaches a suitablepercentage, which may be for instance, from one to ten per cent, part ofthe mother liquor may be Withdrawn from the evaporato'rs and added, asindicated, to I, where it purifies more brine. The exact percentage ofthe NaOH in the mother liquor may be varied to suit operatingconditions. Meanwhile, the' sodium sulphate becomes more concentratedand is removed in a manner to be hereinafter set forth. The purifiedsalt and adheringmother liquor passes to centrifuge 'V II, where themother liquor is separated and the salt is washed either with purifiedneutral brine from XV or by any other suitable method. The neutral brinein XV is obtained by neutralizing brine from III with hydrochloric acidwhich may be made as indicated from hydrogen and chlorine from thechlorine-caustic cells XVI. This neutral brine may, if preferred, beused in the evaporators IV, V and VI as indicated. The washing solutionmay go back to the evaporators.

\Vhen the sodium sulphate concentration has become sufiiciently high inthe mother liquor it is removed by the following procedure: Motherliquor is taken from the evaporators and stored in XIV where it iscooled to about 20 C. This separates out some sodium chloride. The clearsolution then passes through the preeooling coil or the NaOHconcentration higher less sodium sulphate is held in the brine and withthe concentration lower, more is held in the brine. The refri stems XXIIand XXIII may with suitable stirrers and scrapers to keep the crystalsfrom adhering to the sides of the systems. I have found that thesesolutions tend readily to supersaturate with respect to sodium sulphateand I prefer to allow this to take place in the precooling coil XXII andseed the cold solution in XXIII with the hydrated sodium sulphate. Thisprocedure allows most of the cooling to be done in a simple precoolingcoil without scrapers for the sides of the tube, The sodium sulphatedeca-hydrate is se arated from the cold brine by the centri X or othersuitable means, and the cold rine goes to the precoolerwhere it coolsthe incoming brine. From there it may go to I, as indicated. The washwater may go back, as indicated, to IX.

The brine from XIV may also go to XII where it is treated with asolution of sodium hydroxide obtained from the cells XVI through XIIIand XXIV, which separates out sodium sul hate either hydrated oranhydrous, depeniiing on the temperature and com 'tion of the solutionin which it is preclpitated. The sodium sulphate is se arated by thecentrifuge X and the mot er liquor containing an excess of sodiumhydroxide, goes b to I to purify more brine.

The mixture of calcium hydroxide, magnesium hydroxide and otherhydroxides 1n XVII is treated with chlorine, preferably direct from thecells XVI, either before the sludge is washed or after washing. Thissludge will usually contain comparatively large amounts of magnesiumhydroxide. Such percentages may be 10 to 20% or even higher. I havefound that an excellent bleach li nor can be made from this slud e ifthe c orination is stopped before the magnesium hydroxide ischlorinated. If the chlorination is carried too far, large percentagesof chlorates are formed. It has always been considered that largepercenta es of magnesium hydroxide in a bleach slu ge rendered thesludge useless for bleach liquor, but I have discovered that it need notbe detrimental if the chlorination is not carried too far. The magnesiumhydroxide remaining may be converted into various ma gnesium compoundsor mixtures.

The present method of obtaining sodium sulphate-may be used inconjunction with any other salt manufacturing process in which calciumis removed from the brine which, in the resent case, occurs when thebrine is treat with sodium hydroxide.

What I claim is:

1. The process of urifying salt-and obtaming sodium sulp ate whichconsists in treating brine with an excess of sodium hyi,ee7,ee a

droxide obtained from caustib chlorine cells separating out theresultant sludge, conducting portions of the purified brine to thechlorine cells, evaporating the balance of the cyclic process, andwashing the precipitated salt with a neutral brine.

3. The process of obtaining sodium sulphate which consists in removingcalcium from a salt brine, and concentrating and recovering the sodiumsulphate contained therein. y r

4. The process of obtaining sodium sulphate as a. by-product in themanufacture of salt which consists in removing calcium from a saltbrine, allowing sodium sulphate to become concentrated in the brine,cooling portions of the mother liquor to cause sodium sulphate toseparate'out, and using the cold mother liquor to precool other portionsof brine.

5. The process of obtaining sodium sulhate from a brine which consistsin cooling the brine to about 20 C., separating out the precipitatedsalt, cooling the solution to about 0 C., and separating out thehydrated sodium sulphate.

6. The process of obtaining sodium sulphate from a brine which consistsin cooling the brine to about 20 (3., separating out the precipitatedsalt, cooling the solution to about 0 0., separating out the hydratedsodium sulphate, and using the cold mother o liquor to precool anotherportion of brine to become supersaturated with sodium sulphate.-

7. The process of obtaining sodium sulphate from a brine which comprisesfirst re- 115 moving from the brine magnesium and calcium and thentreating the brine with sodium hydroxide to precipitate sodium sulp ate.

8. The process of obtaining sodium sul- 1 phate from a brine whichconsists in treating the brine with sodium hydroxide to precipitatesodium sulphate, separating the sodium sulphate and using the motherliquor to purify an impure salt brine.

9. The process of' purifying salt which consists in treating a brinewith an excess of sodium hydroxide, removing the hydroxides which areprecipitated, evaporating the purified brine, recovering salt therefrom,us- 130 ing the mother liquor with removal of sodium sulphate fortreating more brine in a cyclic process, and Washing the precipitatedsalt with a neutral brine.

10. The process of obtaining sodium sulphate from a brine which consistsin cooling the brine to about 20 0., separating out the precipitatedsalt, cooling the solution to about 0 0., separating out thehydrated'sodium sulphate, using the cold mother liquor 1 to precoolanother portion of brine, and alname to this specification, this 8th dayof 15 April, 1925.

VIc oR YNGVE.

